Probe station

ABSTRACT

A probe station for testing a wafer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.11/083,677, filed Mar. 16, 2005, now U.S. Pat. No. 7,554,322; which is acontinuation of U.S. patent application Ser. No. 09/881,312, filed Jun.12, 2001, now U.S. Pat. No. 6,914,423, which claims the benefit of U.S.Provisional App. No. 60/230,552, filed Sep. 5, 2000

BACKGROUND OF THE INVENTION

The present application relates to a probe station.

BRIEF SUMMARY OF THE INVENTION

With reference to FIGS. 1, 2 and 3, a probe station comprises a base 10(shown partially) which supports a platen 12 through a number of jacks14 a, 14 b, 14 c, 14 d which selectively raise and lower the platenvertically relative to the base by a small increment (approximatelyone-tenth of an inch) for purposes to be described hereafter. Alsosupported by the base 10 of the probe station is a motorized positioner16 having a rectangular plunger 18 which supports a movablechuck-assembly 20 for supporting a wafer or other test device. The chuckassembly 20 passes freely through a large aperture 22 in the platen 12which permits the chuck assembly to be moved independently of the platenby the positioner 16 along X, Y and Z axes, i.e., horizontally along twomutually-perpendicular axes X and Y, and vertically along the Z axis.Likewise, the platen 12, when moved vertically by the jacks 14, movesindependently of the chuck assembly 20 and the positioner 16.

Mounted atop the platen 12 are multiple individual probe positionerssuch as 24 (only one of which is shown), each having an extending member26 to which is mounted a probe holder 28 which in turn supports arespective probe 30 for contacting wafers and other test devices mountedatop the chuck assembly 20. The probe positioner 24 has micrometeradjustments 34, 36 and 38 for adjusting the position of the probe holder28, and thus the probe 30, along the X, Y and Z axes, respectively,relative to the chuck assembly 20. The Z axis is exemplary of what isreferred to herein loosely as the “axis of approach” between the probeholder 28 and the chuck assembly 20, although directions of approachwhich are neither vertical nor linear, along which the probe tip andwafer or other test device are brought into contact with each other, arealso intended to be included within the meaning of the term “axis ofapproach.” A further micrometer adjustment 40 adjustably tilts the probeholder 28 to adjust planarity of the probe with respect to the wafer orother test device supported by the chuck assembly 20. As many as twelveindividual probe positioners 24, each supporting a respective probe, maybe arranged on the platen 12 around the chuck assembly 20 so as toconverge radially toward the chuck assembly similarly to the spokes of awheel. With such an arrangement, each individual positioner 24 canindependently adjust its respective probe in the X, Y and Z directions,while the jacks 14 can be actuated to raise or lower the platen 12 andthus all of the positioners 24 and their respective probes in unison.

An environment control enclosure is composed of an upper box portion 42rigidly attached to the platen 12, and a lower box portion 44 rigidlyattached to the base 10. Both portions are made of steel or othersuitable electrically conductive material to provide EMI shielding. Toaccommodate the small vertical movement between the two box portions 42and 44 when the jacks 14 are actuated to raise or lower the platen 12,an electrically conductive resilient foam gasket 46, preferably composedof silver or carbon-impregnated silicone, is interposed peripherally attheir mating juncture at the front of the enclosure and between thelower portion 44 and the platen 12 so that an EMI, substantiallyhermetic, and light seal are all maintained despite relative verticalmovement between the two box portions 42 and 44. Even though the upperbox portion 42 is rigidly attached to the platen 12, a similar gasket 47is preferably interposed between the portion 42 and the top of theplaten to maximize sealing.

With reference to FIGS. 5A and 5B, the top of the upper box portion 42comprises an octagonal steel box 48 having eight side panels such as 49a and 49 b through which the extending members 26 of the respectiveprobe positioners 24 can penetrate movably. Each panel comprises ahollow housing in which a respective sheet 50 of resilient foam, whichmay be similar to the above-identified gasket material, is placed. Slitssuch as 52 are partially cut vertically in the foam in alignment withslots 54 formed in the inner and outer surfaces of each panel housing,through which a respective extending member 26 of a respective probepositioner 24 can pass movably. The slitted foam permits X, Y and Zmovement of the extending members 26 of each probe positioner, whilemaintaining the EMI, substantially hermetic, and light seal provided bythe enclosure. In four of the panels, to enable a greater range of X andY movement, the foam sheet 50 is sandwiched between a pair of steelplates 55 having slots 54 therein, such plates being slidabletransversely within the panel housing through a range of movementencompassed by larger slots 56 in the inner and outer surfaces of thepanel housing.

Atop the octagonal box 48, a circular viewing aperture 58 is provided,having a recessed circular transparent sealing window 60 therein. Abracket 62 holds an apertured sliding shutter 64 to selectively permitor prevent the passage of light through the window. A stereoscope (notshown) connected to a CRT monitor can be placed above the window toprovide a magnified display of the wafer or other test device and theprobe tip for proper probe placement during set-up or operation.Alternatively, the window 60 can be removed and a microscope lens (notshown) surrounded by a foam gasket can be inserted through the viewingaperture 58 with the foam providing EMI, hermetic and light sealing. Theupper box portion 42 of the environment control enclosure also includesa hinged steel door 68 which pivots outwardly about the pivot axis of ahinge 70 as shown in FIG. 2A. The hinge biases the door downwardlytoward the top of the upper box portion 42 so that it forms a tight,overlapping, sliding peripheral seal 68 a with the top of the upper boxportion. When the door is open, and the chuck assembly 20 is moved bythe positioner 16 beneath the door opening as shown in FIG. 2A, thechuck assembly is accessible for loading and unloading.

With reference to FIGS. 3 and 4, the sealing integrity of the enclosureis likewise maintained throughout positioning movements by the motorizedpositioner 16 due to the provision of a series of four sealing plates72, 74, 76 and 78 stacked slidably atop one another. The sizes of theplates progress increasingly from the top to the bottom one, as do therespective sizes of the central apertures 72 a, 74 a, 76 a and 78 aformed in the respective plates 72, 74, 76 and 78, and the aperture 79 aformed in the bottom 44 a of the lower box portion 44. The centralaperture 72 a in the top plate 72 mates closely around the bearinghousing 18 a of the vertically-movable plunger 18. The next plate in thedownward progression, plate 74, has an upwardly-projecting peripheralmargin 74 b which limits the extent to which the plate 72 can slideacross the top of the plate 74. The central aperture 74 a in the plate74 is of a size to permit the positioner 16 to move the plunger 18 andits bearing housing 18 a transversely along the X and Y axes until theedge of the top plate 72 abuts against the margin 74 b of the plate 74.The size of the aperture 74 a is, however, too small to be uncovered bythe top plate 72 when such abutment occurs, and therefore a seal ismaintained between the plates 72 and 74 regardless of the movement ofthe plunger 18 and its bearing housing along the X and Y axes. Furthermovement of the plunger 18 and bearing housing in the direction ofabutment of the plate 72 with the margin 74 b results in the sliding ofthe plate 74 toward the peripheral margin 76 b of the next underlyingplate 76. Again, the central aperture 76 a in the plate 76 is largeenough to permit abutment of the plate 74 with the margin 76 b, butsmall enough to prevent the plate 74 from uncovering the aperture 76 a,thereby likewise maintaining the seal between the plates 74 and 76.Still further movement of the plunger 18 and bearing-housing in the samedirection causes similar sliding of the plates 76 and 78 relative totheir underlying plates into abutment with the margin 78 b and the sideof the box portion 44, respectively, without the apertures 78 a and 79 abecoming uncovered. This combination of sliding plates and centralapertures of progressively increasing size permits a full range ofmovement of the plunger 18 along the X and Y axes by the positioner 16,while maintaining the enclosure in a sealed condition despite suchpositioning movement. The EMI sealing provided by this structure iseffective even with respect to the electric motors of the positioner 16,since they are located below the sliding plates.

With particular reference to FIGS. 3, 6 and 7, the chuck assembly 20 isa modular construction usable either with or without an environmentcontrol enclosure. The plunger 18 supports an adjustment plate 79 whichin turn supports first, second and third chuck assembly elements 80, 81and 83, respectively, positioned at progressively greater distances fromthe probe(s) along the axis of approach. Element 83 is a conductiverectangular stage or shield 83 which detachably mounts conductiveelements 80 and 81 of circular shape. The element 80 has a planarupwardly-facing wafer-supporting surface 82 having an array of verticalapertures 84 therein. These apertures communicate with respectivechambers separated by O-rings 88, the chambers in turn being connectedseparately to different vacuum lines 90 a, 90 b, 90 c (FIG. 6)communicating through separately-controlled vacuum valves (not shown)with a source of vacuum. The respective vacuum lines selectively connectthe respective chambers and their apertures to the source of vacuum tohold the wafer, or alternatively isolate the apertures from the sourceof vacuum to release the wafer, in a conventional manner. The separateoperability of the respective chambers and their corresponding aperturesenables the chuck to hold wafers of different diameters.

In addition to the circular elements 80 and 81, auxiliary chucks such as92 and 94 are detachably mounted on the corners of the element 83 byscrews (not shown) independently of the elements 80 and 81 for thepurpose of supporting contact substrates and calibration substrateswhile a wafer or other test device is simultaneously supported by theelement 80. Each auxiliary chuck 92, 94 has its own separateupwardly-facing planar surface 100, 102 respectively, in parallelrelationship to the surface 82 of the element 80. Vacuum apertures 104protrude through the surfaces 100 and 102 from communication withrespective chambers within the body of each auxiliary chuck. Each ofthese chambers in turn communicates through a separate vacuum line and aseparate independently-actuated vacuum valve (not shown) with a sourceof vacuum, each such valve selectively connecting or isolating therespective sets of apertures 104 with respect to the source of vacuumindependently of the operation of the apertures 84 of the element 80, soas to selectively hold or release a contact substrate or calibrationsubstrate located on the respective surfaces 100 and 102 independentlyof the wafer or other test device. An optional metal shield 106 mayprotrude upwardly from the edges of the element 83 to surround the otherelements 80, 81 and the auxiliary chucks 92, 94.

All of the chuck assembly elements 80, 81 and 83, as well as theadditional chuck assembly element 79, are electrically insulated fromone another even though they are constructed of electrically conductivemetal and interconnected detachably by metallic screws such as 96. Withreference to FIGS. 3 and 3A, the electrical insulation results from thefact that, in addition to the resilient dielectric O-rings 88,dielectric spacers 85 and dielectric washers 86 are provided. These,coupled with the fact that the screws 96 pass through oversizedapertures in the lower one of the two elements which each screw joinstogether thereby preventing electrical contact between the shank of thescrew and the lower element, provide the desired insulation. As isapparent in FIG. 3, the dielectric spacers 85 extend over only minorportions of the opposing surface areas of the interconnected chuckassembly elements, thereby leaving air gaps between the opposingsurfaces over major portions of their respective areas. Such air gapsminimize the dielectric constant in the spaces between the respectivechuck assembly elements, thereby correspondingly minimizing thecapacitance between them and the ability for electrical current to leakfrom one element to another. Preferably, the spacers and washers 85 and86, respectively, are constructed of a material having the lowestpossible dielectric constant consistent with high dimensional stabilityand high volume resistivity. A suitable material for the spacers andwashers is glass epoxy, or acetyl homopolymer marketed under thetrademark Delrin by E. I. DuPont.

With reference to FIGS. 6 and 7, the chuck assembly 20 also includes apair of detachable electrical connector assemblies designated generallyas 108 and 110, each having at least two conductive connector elements108 a, 108 b and 110 a, 110 b, respectively, electrically insulated fromeach other, with the connector elements 108 b and 110 b preferablycoaxially surrounding the connector elements 108 a and 110 a as guardstherefor. If desired, the connector assemblies 108 and 110 can betriaxial in configuration so as to include respective outer shields 108c, 110 c surrounding the respective connector elements 108 b and 110 b,as shown in FIG. 7. The outer shields 108 c and 110 c may, if desired,be connected electrically through a shielding box 112 and a connectorsupporting bracket 113 to the chuck assembly element 83, although suchelectrical connection is optional particularly in view of thesurrounding EMI shielding enclosure 42, 44. In any case, the respectiveconnector elements 108 a and 110 a are electrically connected inparallel to a connector plate 114 matingly and detachably connectedalong a curved contact surface 114 a by screws 114 b and 114 c to thecurved edge of the chuck assembly element 80. Conversely, the connectorelements 108 b and 110 b are connected in parallel to a connector plate116 similarly matingly connected detachably to element 81. The connectorelements pass freely through a rectangular opening 112 a in the box 112,being electrically insulated from the box 112 and therefore from theelement 83, as well as being electrically insulated from each other. Setscrews such as 118 detachably fasten the connector elements to therespective connector plates 114 and 116.

Either coaxial or, as shown, triaxial cables 118 and 120 form portionsof the respective detachable electrical connector assemblies 108 and110, as do their respective triaxial detachable connectors 122 and 124which penetrate a wall of the lower portion 44 of the environmentcontrol enclosure so that the outer shields of the triaxial connectors122, 124 are electrically connected to the enclosure. Further triaxialcables 122 a, 124 a are detachably connectable to the connectors 122 and124 from suitable test equipment such as a Hewlett-Packard 4142B modularDC source/monitor or a Hewlett-Packard 4284A precision LCR meter,depending upon the test application. If the cables 118 and 120 aremerely coaxial cables or other types of cables having only twoconductors, one conductor interconnects the inner (signal) connectorelement of a respective connector 122 or 124 with a respective connectorelement 108 a or 110 a, while the other conductor connects theintermediate (guard) connector element of a respective connector 122 or124 with a respective connector element 108 b, 110 b. U.S. Pat. No.5,532,609 discloses a probe station and chuck and is hereby incorporatedby reference.

The foregoing and other objectives, features, and advantages of theinvention will be more readily understood upon consideration of thefollowing detailed description of the invention, taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a partial front view of an exemplary embodiment of a waferprobe station constructed in accordance with the present invention.

FIG. 2 is a top view of the wafer probe station of FIG. 1.

FIG. 2A is a partial top view of the wafer probe station of FIG. 1 withthe enclosure door shown partially open.

FIG. 3 is a partially sectional and partially schematic front view ofthe probe station of FIG. 1.

FIG. 3A is an enlarged sectional view taken along line 3A-3A of FIG. 3.

FIG. 4 is a top view of the sealing assembly where the motorizedpositioning mechanism extends through the bottom of the enclosure.

FIG. 5A is an enlarged top detail view taken along line 5A-5A of FIG. 1.

FIG. 5B is an enlarged top sectional view taken along line 5B-5B of FIG.1.

FIG. 6 is a partially schematic top detail view of the chuck assembly,taken along line 6-6 of FIG. 3.

FIG. 7 is a partially sectional front view of the chuck assembly of FIG.6.

FIG. 8 illustrates an adjustment plate and a surrounding positionalstage.

FIG. 9 illustrates an extended positional stage.

FIG. 10 illustrates a locking mechanism for the positional stage.

FIG. 11 illustrates a locking mechanism for the adjustment plate and atab for rotational engagement of the adjustment plate.

FIG. 12 illustrates traditional adjustment of the orientation of thechuck.

FIG. 13 illustrates a modified adjustment of the orientation of thechuck.

FIG. 14 illustrates a probe station supported by an isolation stage,both of which are surrounded by a frame.

FIG. 15 illustrates the engagement of the sides of the environmentalcontrol enclosure.

FIG. 16 illustrates the engagement of a door to the environmentalcontrol enclosure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

The probes may be calibrated by using test structures on the calibrationsubstrates supported by the auxiliary chucks 92 and 94. Duringcalibration the chuck assembly 20, as previously described in thebackground, is normally aligned with the probes. A wafer placed on thechuck assembly 20 is not normally accurately aligned with the auxiliarychucks 92 and 94, and hence the probes. In order to test the wafer theentire chuck assembly 20, including the auxiliary chucks 92 and 94, isrotated to align the wafer with the positioners 24 and their respectiveprobes. Typically, during testing the chuck assembly 20 is rotated torealign the test structures on the calibration substrates supported bythe auxiliary chucks 92 and 94 with the probes. After furthercalibration, the entire chuck assembly 20, including the auxiliarychucks 92 and 94, is again rotated to align the wafer with thepositioners 24 and their respective probes. Unfortunately, the thetaadjustment of the chuck assembly 20 may not be sufficiently accurate forincreasingly small device structures. Multiple theta adjustments of thechuck assembly 20 may result in a slight misalignment of the chuckassembly 20. As a result of such misalignment it may become necessaryfor the operator to painstakingly manually adjust the theta orientationof the chuck assembly 20.

Smaller environmental control enclosures require less time to createsuitable environmental conditions within the environmental controlenclosure for accurate measurements. The environmental control enclosureis sufficiently large to permit the chuck assembly to move the entirewafer under the probes for testing. However, if the chuck assembly 20 isrotatable with respect to the environmental control enclosure then theenvironmental control enclosure needs additional width to prevent thecorners of the chuck assembly 20 from impacting the sides of theenvironmental control enclosure.

Normally the encoders within the stage supporting the chuck assemblyinclude software based compensation for non-proportional movement toachieve accurate movement in the X and Y directions over the entirerange of movement. The software compensation of the encoders alsodepends on the X and Y position of the chuck relative to the probes. Inother words, at different X and Y positions over the entire range ofmovement of the chuck the amount of compensation provided to theencoders may vary. This variable compensation depending on the X and Yposition of the chuck results in complicated spatial calculations forappropriate encoder control. The spatial calculations are furthercomplicated when the chuck is rotated to accommodate the auxiliary chuckcalibration.

To overcome the limitations associated with misalignment of the thetaorientation of the wafer, to reduce the size of the environmentalcontrol enclosure, and/or to simplify the compensation for the encodersover the X and Y movement, the present inventors came to the realizationthat the chuck supporting the wafer should rotate with respect to theauxiliary chuck, as illustrated by FIG. 8. FIG. 8 illustrates theadjustment plate 182 and a surrounding positional stage 184.Accordingly, auxiliary chucks 180 preferably maintain a fixed X and Yorientation with respect to the probe positioners and their respectiveprobes. In this manner, the auxiliary chucks are always properlyorientated with the probes positioners and the probes. During use, thechuck (supported by the adjustment plate 182) with a wafer thereon isrotated to the proper theta position with respect to the probes forprobing the wafer. Thereafter, the theta adjustment of the chuck mayremain stationary during subsequent probing of the wafer andrecalibration using the auxiliary chucks. In this manner, typically thechuck assembly needs to only be moved in X, Y, and potentially Zdirections to achieve complete probing of an entire wafer. Accordingly,the environmental control enclosure does not necessarily need to besufficiently wide to accommodate rotation of the positional stage. Also,the encoder compensation may be simplified.

During probing with the chuck assembly 20, as described in thebackground, it became apparent that probing toward the edges of thewafer tended to result in “wobble” of the wafer and chuck assembly 20.In addition, some existing probe assemblies include the chuck assemblyelements supported by a set of linear bearings that permit the upperchuck assembly elements together with the bearing to be slid out of theenvironment enclosure for loading the wafer onto the chuck assembly. Theresulting structure is heavy, and positioned on top of and supported bya plunger affixed to the top of the Z-axis movement of the chuckassembly 20.

To reduce the wobble occurring during probing and reduce the stressapplied to the plunger, the present inventors developed a modifiedarrangement to nearly eliminate the vertical loads on the plunger.Referring to FIG. 9, a modified arrangement includes a central plunger200 providing rotational movement to the adjustment plate 182 and hencea chuck supported thereon. The central plunger 200 may include areceptacle 201 that moves within a tab 203. The positional stage 184 andauxiliary chucks 180 are supported by the stage 204 surrounding thecentral plunger 200 which provides the X, Y, and Z movement. Preferably,the stage includes the central plunger 200. The positional stage 184includes an internal bearing (not shown) upon which the adjustment plate182 rotates. Accordingly, the positional stage 184 is the primary loadbearing member for the adjustment plate 182 and chuck thereon. Spacedapart linear bearings 206 provide a vertical and lateral load bearingsupport to the rotational chuck while the central plunger 200 providesthe rotational movement to the chuck without (free from) being theprimary load bearing member. The plunger 200 preferably maintainssubstantially constant vertical position with respect to the adjustmentplate 182 when the stage 204 provides vertical “Z” movement of thepositional stage.

Unlocking a lock permits the positional stage 184, including therotational chuck, to slide out of the probe station for easier placementof wafers thereon. Normally when the positional stage 184 is extended,the wafer thereon is adjusted or otherwise replaced with a differentwafer for subsequent testing. After repeated movement of the stage inand out of the probe station, together with rotational movement of thechuck (theta adjustment), the present inventors determined that theresulting theta movement of the chuck may be significantly differentthan the initial “zero” theta. In other words, after repeated use theadjustment plate 182 may be offset by a significant theta offset. Suchsignificant potential theta offset may result in the cabling to thechuck, normally provided by a rollout service loop, being wound aboutthe chuck assembly creating a significantly greater tension thereon orotherwise damaging the cabling or chuck. The adjustment plate 182 mayinclude a rotational theta limit about “zero” to minimize potentialdamage. A suitable rotational limit may be .±.7.5 degrees. A furtherlimitation exists in the case that the adjustment plate 182 is rotatedto a position near its rotational limit because the user may not bepermitted further rotational movement in that direction when aligninganother wafer thereby resulting in frustration to the user. To overcomethese limitations the rotational orientation of the adjustment plate 182(chuck) is returned to “zero” prior to sliding the positional stage 184out of the probe station. In this manner, the chuck is always at aconstant rotational position, such as 0 degrees, when a wafer ispositioned thereon so that the likelihood of damaging the probe stationby unintended tension on the wires and other interconnections to thechuck assembly is reduced. In addition, the range where the chuck isorientated prior to sliding out the positional stage 184 may be anypredefined range of values. Also, the user maintains the ability torotate the adjustment plate 182 as necessary during further alignment.

While the positional stage 184 is extended the user may attempt torotate the adjustment plate 182. Unfortunately, this may result indifficulty engaging the tab 203 with the receptacle 201 when thepositional stage 184 is retracted. This difficulty is the result of therotation of the lunger 200 not likewise rotating the positional stage asin existing designs.

Referring to FIG. 10, the “zero” theta lockout may be provided by amechanical arrangement together with a locking mechanism. A rotationalhandle 210 is secured to the upper plate 212 of the positional stage184. A block 216 as secured to the lower plate 214 of the positionalstage 184, which is rigidly attached to the housing 204. A finger 218 isinserted within a slot 220 defined by the block 216 to rigidly lock theupper plate 212 in position. The handle 210 is rotated to remove thefinger 218 from the slot 220 to permit relative movement of the upperplate 212 with respect to the lower plate 214.

Referring to FIG. 11, the handle 210 includes a shaft 230 with a slot232 in the end thereof. With the handle 210 in the closed position, theslot 232 is aligned with an alignment plate 234 attached to the rear ofthe adjustment plate 182. The adjustment plate 182 may be rotated toproperly align the wafer thereon, with the alignment plate 234 travelingwithin the slot 232. To unlock the handle 210 the adjustment plate 182is realigned to “zero” thus permitting rotational movement of the handle210, while simultaneously preventing rotational movement (substantiallyall) of the adjustment plate 182. It is to be understood that anysuitable lock out mechanism may likewise be used.

When one or more chuck assembly elements are supported by the adjustmentplate 182, the upper surface of the chuck assembly should have asuitable orientation with respect to the probes, such as co-planar.Referring to FIG. 12, to adjust the orientation of the chuck assembly,the positional stage 184 is extended to provide convenient access toloosen threaded screws 240. The threaded screws 240 interconnect thechuck to the adjustment plate 182. Next an adjusting screw 242, such asa jack screw, is rotated to adjust the spacing between the adjustmentplate and the chuck. Then the threaded screw 240 is tightened to rigidlysecure the adjustment plate to the chuck. The positional stage is thenslid back into the probe station and locked in place. At this point theactual orientation of the upper surface of the chuck assembly may bedetermined. Normally, the positional stage is adjusted several times toachieve accurate orientation. Unfortunately, this trial and errorprocess of extending the positioning stage from the probe station,adjusting the orientation of the upper surface of the chuck assembly byadjusting one or more adjusting screws 242, and repositioning thepositioning stage in the probe station, may take considerable time.

After consideration of this prolonged process of adjusting theorientation of the upper surface of the probe assembly, the presentinventors came to the realization that loosening the threaded screw 240relaxes the chuck from the adjustment plate 182. The amount ofrelaxation is hard to determine because the weight of the chuck assemblywould make it appear that the chuck, jack screw, and adjustment plateare held together. Also, by adjusting the jack screw 242 and measuringthe resulting movement of the chuck assembly provides an inaccurateresult. In order to reduce the relaxation of the chuck and theadjustment plate, the present inventors determined that the threadedscrew 240 should be tensioned so that the chuck does not significantlyrelax with respect to the adjustment plate. Referring to FIG. 13, onetechnique to tension the threaded screw is to provide a set of springs250 under the head of the screw to provide an outwardly pressing forcethereon when the threaded screw 240 is loosened. In this manner therelaxation between the chuck and the adjustment plate is reduced,resulting in a more accurate estimate of the adjustment of theorientation of the upper chuck assembly element. This reduces thefrustration experienced by the operator of the probe station in properlyorientating the chuck assembly. In addition, by loosening the threadedscrews slightly, the chuck assembly may be more easily oriented byadjusting the jack screws while the probe station is in its lockedposition within the probe station. Thereafter, the positioning stage isextended and the threaded screws are tightened. It is to be understoodthat any structure may likewise be used to provide tension between thechuck assembly element and the adjustment plate while allowingadjustment of the spacing between the adjustment plate and the chuckassembly element, or otherwise adjusting the orientation of the chuck.

Normally it is important during testing to isolate the probe stationfrom the earth and other nearby devices that may impose vibrations orother movement to the probe station, and hence the device under test.With proper isolation, the probe station may provide more accuratemeasurements. Typically the probe station is placed on a flat tablehaving a surface somewhat larger than the probe station itself toprovide a stable surface and reduce the likelihood of inadvertentlysliding the probe station off the table. The table includes isolation,such as pneumatic cylinders, between the floor and the table surface.Also, it is difficult to lift the probe station onto the table in acontrolled manner that does not damage the table and/or probe station.Further, the probe station is prone to being damaged by being bumped.

To overcome the aforementioned limitations regarding the size of theprobe station, the present inventors came to the realization that anintegrated isolation stage, probe station, and frame provides thedesired benefits, as illustrated in FIG. 14. The integrated isolationstage and probe station eliminates the likelihood of the probe stationfalling off the isolation stage. The top of the isolation stage maylikewise form the base for the probe station, which reduces the overallheight of the probe station, while simultaneously providing a stablesupport for the probe station. To protect against inadvertently damagingthe probe station a frame at least partially surrounds the isolationstage and the probe station.

Even with extensive shielding and guarding existing environmentalenclosures still seem to be inherently prone to low levels of noise.After consideration of the potential sources of noise, the presentinventors determined that the construction of the environmental controlenclosure itself permits small leakage currents to exist. Existingenvironmental control enclosures include one plate screwed or otherwiseattached to an adjoining plate. In this manner, there exists a straightline path from the interior of the environmental control enclosure tooutside of the environmental control enclosure. These joints are alsoprone to misalignment and small gaps there between. The gaps, orotherwise straight paths, provide a convenient path for leakagecurrents. Referring to FIGS. 15 and 16, to overcome the limitation ofthis source of leakage currents the present inventors redesigned theenvironmental control enclosure to include all (or substantial portion)joints having an overlapping characteristic. In this manner, the numberof joints that include a straight path from the interior to the exteriorof the environmental control enclosure is substantially reduced, orotherwise eliminated.

The terms and expressions which have been employed in the foregoingspecification are used therein as terms of description and not oflimitation, and there is no intention, in the use of such terms andexpressions, of excluding equivalents of the features shown anddescribed or portions thereof, it being recognized that the scope of theinvention is defined and limited only by the claims which follow.

1. An enclosure for a probe station comprising: (a) a plurality of atleast four side walls, one of said side walls comprising a side plate;(b) a first plate including a first surface comprising one of a topsurface and a bottom surface of an interior of said enclosure; (c) asecond plate including a second surface comprising the other of said topsurface and said bottom surface of said enclosure, said second plateaffixed to said side plate with a substantially planar surface of saidsecond plate in contact with a substantially planar surface of said sideplate, wherein the joint between said second plate and said side plateis substantially free from straight line paths between the interior ofsaid enclosure to the exterior of said enclosure at locations where saidsecond plate and said side plate are in contact with one another.
 2. Theenclosure of claim 1 wherein said at least one of said side walls is notdoor a of said enclosure.
 3. The enclosure of claim 1 wherein all ofsaid four side wails are side plates and the locations where said secondplate and all four side plates are in contact with one another are issubstantially free from straight line paths between the interior of saidenclosure to the exterior of said enclosure at locations.
 4. Anenclosure for a probe station comprising: (a) a plurality of at leastfour side walls; at least one of said side walls comprising a side plateincluding a side surface on an interior of said enclosure; (b) a firstplate including a first surface comprising one of a top surface and abottom surface of said interior of said enclosure; and (c) a secondplate including a second surface comprising the other of said topsurface and said bottom surface of said enclosure, wherein said secondplate and said side plate are affixed to each other and one of said sidesurface and said second surface includes a joint surface portion offsetfrom said surface of said interior toward an exterior of said enclosureand in contact with a substantially planar surface of the other of saidside plate and said second plate so that the joint between said secondplate and said side plate is substantially free from straight line pathsbetween the interior of said enclosure to the exterior of said enclosureat locations where said second plate and said side plate are on contactwith one another.
 5. The enclosure of claim 4 wherein said at least oneof said side walls is not a door of said enclosure.
 6. The enclosure ofclaim 4 wherein said joint between said second plate at all of said fourside walls is substantially free from straight line paths between theinterior of said enclosure to the exterior of said enclosure atlocations where said second plate and said four sidewalls are in contactwith one another.
 7. An enclosure for a probe station comprising: (a) aplurality of side walls, at least one of said side walls comprising aside plate and at least one of said side walls is a door to saidenclosure; (b) a top plate affixed to said side plate with asubstantially planar surface in contact with a substantially planarsurface of said side plate and (c) a bottom plate affixed to said sideplate with a substantially planar surface in contact with asubstantially planar surface of said side plate; (d) wherein the jointsbetween said top and said bottom plates and said door are substantiallyfree from straight line paths between the interior of said enclosure tothe exterior of said enclosure at locations where said top and bottomplates and said door are in contact with one another.
 8. The enclosureof claim 7 wherein said joint between said door and two side walls issubstantially free from straight line paths between the interior of saidenclosure to the exterior of said enclosure at locations where said doorand said two side walls are in contact with one another.